Bachmann & Casal (1962a) and Castro et al. 1959 (1960) used the name Culex virgultus Theobald for bidens. They followed Lane (1953) who synonymized bidens under virgultus. However, Bram (1967) not only resurrected bidens, based on the male genitalia being distinct from virgultus, but also synonymized Culex interfor Dyar with bidens. The holotype male of interfor was collected on a train between Tucumán and Jujuy, (Belkin et al. 1968; Knight & Stone 1977). Stone (1956 (1957)) synonymized Culex virgultus under Culex declarator Dyar & Knab." (Mitchell & Darsie, 1985).
Disease relations: Culex bidens was suspected to be the vector of Eastern Equine Encephalitis virus during the epizootic in Chaco Province, Argentina in 1988 (Sabattini et al. 1998).
Immature stages were collected in permanent natural pools originated by rainfalls or overflowing, between rocks; in backwater of rivers. Sites presented great sun exposure and abundant semi-submerged vegetation.